This invention relates to a light stable polymeric laminate and method of preparation, and more particularly to a polystyrene-polymethylmethacrylate laminate formed by the interfacial bonding of a functionalized styrenic copolymer to a polymer having pendant ester groups such as polymethylmethacrylate.
General purpose polystyrene (GPPS) has optical and mechanical properties similar to polymethylmethacrylate (PMMA) when it is protected from ultraviolet light. Further, GPPS is readily thermoformable into a number of shapes. Unlike polymethylmethacrylate however, GPPS is light sensitive and undergoes photo-induced oxidative degradation at its surface. This results in a yellowing and embrittling of the polymer after prolonged exposure to ultraviolet light. Because of this sensitivity to ultraviolet light, GPPS's use for exterior applications such as insulating glazing for residential and commercial windows or other indoor or outdoor applications where it is likely to be exposed to ultraviolet light is quite limited.
Currently, the market for light stable outdoor glazing applications is dominated by acrylics such as PMMA because of its optical transparency and light stability. Polycarbonate has also found use for applications which require high impact resistance. However, the cost of acrylics is approximately twice or more than that of GPPS. Polycarbonate is also expensive.
Attempts have been made to protect polystyrene from the effects of ultraviolet light by laminating it to a light stable material such as PMMA. See, for example, "Light-Stable PS Sheet on the Way", Plastic World. October 1982, page 5. However, it is known that acrylics such as PMMA do not adhere to general purpose crystalline polystyrene due to their incompatibility. Without an intervening adhesive layer, a laminate of GPPS and PMMA can be easily delaminated by applying only a small external force. Use of intervening adhesive layers such as urethane or epoxy-based adhesives is possible. However, such adhesives exhibit undesirable optical properties such as opacity or haziness.
Others have used copolymers of styrene in forming laminates with acrylics. For example, Hall, U.S. Pat. No. 4,350,742, teaches bonding an acrylic film directly to poly(styrene-co-acrylic acid) (SAA). However, the SAA copolymer is even more prone to rapid ultraviolet degradation than polystyrene itself. Thus, an SAA copolymer would be poorly suited to exterior applications, even when laminated to an acrylic.
Accordingly, the need still exists in the art for a light stable, optically clear material which is less expensive than acrylics or polycarbonate. Further, the need still exists in the art for a light stable yet inexpensive low heat transfer material for residential and commercial glazing applications. Still further, the need exists in the art for a process of bonding together incompatible styrenic and acrylic polymers without the need for intervening glues or adhesives.